This invention is related to tools for use inside a wellbore and more specifically to an apparatus for pulling a logging cable and logging device down into a deviated borehole.
When drilling from offshore drilling platforms, it is usually the established practice to drill outward from the tower in many different directions, so as to best utilize the platform. The result is that most of the wellbores do not go straight down but extend downward and outward at an angle from vertical. These deviated boreholes create different problems than those encountered in conventional onshore drilling operations. One problem encountered when trying to survey these boreholes, occurs when a logging tool is lowered down the borehole. Since the borehole is usually drilled at quite an angle, often up to seventy degrees from vertical, the force of gravity on a logging tool and logging cable is not sufficient to overcome the friction encountered by the tool and cable against the side of the borehole. Often, many man hours of work are lost in trying to force the logging tool to the bottom of the borehole. It is therefore desirable to have some type of a tool which will aid the logging tool in its descent down through the wellbore.
Several kinds of pulling devices have been tried in the past. However, none of these have proved to be effective. These designs include crawling and vibrating devices as well as attempts to use stiff cables or drilling mud to push the equipment down the borehole.